Existing control devices, counters for example, as shown in FIGS. 19 and 20 consist of a front display assembly 40, a base 57, a front panel 42, upper and lower panels 43 and 44, and left and right panels 45 and 46.
The front display assembly 40 has a front casing 47, which includes a square case 48. On the front of square case 48 is a numeric display 49, and below this display 49 are two (2) horizontal rows of keyholes 50 and 51. The back of square case 48 is molded to accept installation of switch mechanisms.
Extending from the four corners at the back of the square case 48 are four hooks 52 that cooperate with the printed circuit board assembly. The hooks 52 are rectangular in shape, and each has a horizontal slot 52a provided in a center portion thereof. In the center of its upper and lateral surfaces, the case 48 has hooks 53, each of which is provided with a slot 53c. A front panel 42 of the printed circuit board assembly is provided at its top and sides with tabs 54, which engage with the slots 53c of hooks 53.
A liquid crystal display ("LCD") 55 is inserted into the front casing 47, and rubber connectors 56 are inserted into grooves (not pictured) in front casing 47 and LCD 55. A backlight 55a is pushed in the front casing 47, and front panel 42 is inserted and locked into front casing 47 when the tabs 54 on the top and sides of the front panel 42 engage in the slots 53c of the hook of the top and sides of the case 48. The front panel 42 is then soldered to backlight 55a and LCD 55.
A base 57 is attached to printed boards 43, 44, 45 and 46 to form the printed circuit board assembly, and the circuit board assembly is then fitted into the front assembly 40. Tabs 43a and 44a on upper and lower boards 43 and 44 fit into slots 52a on hooks 52. Subsequently, the front panel 42 is soldered via solder bridges to a remaining portion of the printed circuit board assembly in the particular method of assembly.
In the existing control device described above, the hooks 53 had a considerable width. Thus, a large portion of the sides were dedicated to their use blocking access to the printed circuit board assembly from the sides of the device after full assembly. This makes it difficult to secure sufficient space for any number of solder bridges 63, as shown in FIG. 21, or impossible to install, for example dipswitches or other electronic components on the front panel 42, due to the need for access to these components after the final assembly for changing operating mode.
Alternatively, the hooks 53 as shown in FIGS. 22 and 23 are sometimes used in order to efficiently use the sides of the front panel 42 and provide easy access from the sides thereto. However, to mold the projections 53b on hooks 53, holes 62 must be provided in numeric display 49 on the front of case 48, as shown in FIG. 23. In addition to being unsightly, these holes make it difficult to insure that the front panel is watertight.
Further, in the existing device the keys on the front display are configured in two (2) narrow rows making it difficult to selectively actuate a key in one row without also inadvertently actuating a corresponding key in the other row with the finger tip of the person making key selections. In addition, the existing keys are defined by rectangular parallelograms having a flat upper surface again increasing the chance of inadvertent selection of keys. The present invention overcomes this particular problem by changing the configuration of the upper surface to be beveled to be explained in detail below.
Further, the existing control devices are difficult to adjust the mode of operation.
As shown in FIG. 24, the face 101a of case 101 has a key panel 102 with keys for setting numerical values, and a display 4 and 5 for displaying present values and set values, respectively, consisting of seven-segment LEDs.
Inside the case 101 is a built-in mode switch (not shown), which is covered by cover C. This mode switch may consist of, for example, dipswitches connected to a control circuit for input and output such as a one-chip microprocessor. The mode switch is used to switch among the various modes including input mode, output mode, maximum counting speed, one-shot output time, and so on.
With this type of control device, the user cannot adjust the timing at which signals are received from or sent to other devices, nor can he set or change the value for the one-shot output time, which controls the operating time of the output actuator. Rather, the various initial values of the control device are set at the factory. This being the case, it is often necessary to set or change the auxiliary values. The existing devices have several schemes by which the user can change these settings. A first scheme is to provide a continuously variable control mounted on the device, a second scheme is to have dipswitches on the device, and a third scheme is to provide a mode key on the front of the case to switch among the setting modes for auxiliary values so that each value can be entered in its own mode.
In existing control devices of the type described above, the user must confirm that the dipswitches or other switching devices have indeed been switched to the correct mode by removing a cover C, as shown in FIG. 24, and viewing the position of the switches through the opening in case 101. Generally, control devices A such as counters have their display assembly 101a and value setting device 102 on front panel 101a. Only the front panel 101a is exposed in the control panel B while the rest of the control device is located behind the control panel B making it difficult to access and exposed on the front surface of the case. Thus, whenever the user desires to check the position of the dipswitches or settings on other electronic components (i.e. mode), the user must remove the control device from the control panel and then open the cover C of the control device to view the setting on the electronic component.
If the aforesaid control device A is permanently mounted to control panel B, or if the aforesaid cover C of the control device is locked in place by means of mounting clip D, it is not possible to check the settings until after removing the control device A from control panel B. Thus, checking the settings by disassembling the control device is a laborious and time-consuming operation.
In other existing devices, when a variable control is used to set and change auxiliary values such as the aforesaid one-shot output time, it is easy to fine-tune the settings. However, the accuracy of the values is poor, and are liable to change due to the influence of external factors such as temperature. When dipswitches are used, the user must select one from at most two to ten predetermined values, so more precise settings for the auxiliary values are not possible. When using a mode key on the front of the case, which tends to be used infrequently, it raises the possibility of the switch being operated accidentally, or of the values being changed as a joke or prank. This could cause an entire system to malfunction.